Biological membranes Flashcards
2.1.5
What are the function of mebranes within cells?
- Site of chemical reactions - provides attachment sites for enzymes and pigments
- Compartmentalisation - isolation of chemical reactions eg lysosome mebranes isolate hydrolytic enzymes
- Provide internal transport system
- Controls the movement of sunbstances into/out organelles
What is the function of cell surface membranes ?
- Selectively permeable barrier
- Cell signalling
- Cell recognition
- cell to cell adhesion to form tissues
- Enzyme attachment
What is the function of cholesterol?
Steriod
* Connect phospholipids
* Reduces movement of phospholipids giving the membrane stability and flexibilty
* Regulates lateral movement of phospholipids
What is the function of glycocalyx ( glycoprotein + glycolipids)?
glycolipds - carbohydrate attached to phospholipds
glycoproteins - carbohydrate attached to proteins
* Receptor sites - hormones
* cell marker
* Acts as anitgen
* helps cells adhere to one another forming tissue
* forms hydrogen bonds with water to stabilise the membrane
What is the function of proteins?
- structural support
- transport
- helps cell adhere together
- receptors for hormones
What is the function of phospholipds?
- Gives membrane fluidity
- barrier to larger water solube molecules and ions
- lipid soluble (hydrophobic/non polar ) molecules to pass through
- unsaturated fatty acids have kinks in them which prevents close packing , allowing movement of phospholipid within the bilayer . This makes the membrane more fluid and permeable
What 3 factors affect membrane permeability?
- Temperature: High temperature cause more kinetic energy so the membrane protein denature and the phospholipis move further affect - more permeable
- Ph - changes tertiary structure of membrane proteins
- organic solvent- dissolves the membrane so more permeable
What is diffusion?
Diffusion is the net movement of molecules or ions from a region of their higher concentration to a region of their lower concentration
Name 6 factors that affect diffusion
- Temperature : higher temperatures means more kinetic energy so diffusion happens faster
- Surface area : the greater th surface area thre more molecules that can cross the mebrane at anytime
- Concentration gradient : The bigger difference between thte two sides of the membrane the quicker the rate of diffusion
- Distance : The shorter the distance , the faster the rate of diffusion
- Stirring/ moving : More kinetic energy increase the rate of diffusion
- Type of molecule : larger molecule need more energy to move so they tend to diffuse more slowly and non polar molecules can move through the phospholipds bilayer quickly
What is simple diffusion?
Net movement of small, lipid solube molecules directly through the bilayer from an area of high concentration to an area of lower concentration down a concentration gradient
Passive process requires no energy from ATP
Examples : steriods, fat solube vitamins
What is facilated diffusion?
- Passive movent of molecules or ions through a channel or carrier protein from a higher to lower concentration
How do channel proteins work?
- ions are charged and have hydrophilic lining
- can sometimes be gated
- specfic for certain ions
- Special channel proteins called aquaporins allow water to diffuse across the membrane
How do carrier proteins work?
- Specific large polar molecules
- glucose and amino acids
- when the specific molecule binds to the protein , it changes shape and allows molecule across the membrane
What is osmosis?
The net movement of water from a region of higher water potential to a region of lower water potential down a water potential gradient across a partially permeable membrane
What is water potential?
- The tendency of water molecules to leave a solution
- pressure created by water molecules in kPa
- the water potential of pure water = 0
- more solute = more negative
